Update the Wayland core protocol spec file and add support for the new axis_value120 event to handle high resolution scroll wheels.
The axis_value120 replaces the axis_discrete event, which is no longer sent as of version 8 of the protocol. Note that unlike the axis_discrete event, no mention in the spec is made regarding how many axis_value120 events may occur per-axis per-frame, so the values are accumulated and committed when the pointer frame event occurs.